CN115951338A - A method and system for calibrating DTOF lidar - Google Patents

Abstract

The invention discloses a method and a system for calibrating a DTOF laser radar, wherein the calibration method comprises the following implementation steps: additionally arranging a protective outer cover: adding a protective outer cover at a distance R from the DTOF laser radar; acquiring a reference signal and a target signal: the DTOF laser radar emits laser, and a photon detector detects and obtains and stores reflected signals of the protective outer cover and the target position as a reference signal T1 and a target position signal T2; calculating to obtain the actual distance of the target: based on the distance resolution LSB of the TDC of the laser radar in one unit time, the actual distance of the target object is obtained by adopting the following formula to complete calibration; l = (T2-T1) × LSB + R. The invention completes the distance calculation calibration of the DTOF laser radar by utilizing the radar outer cover, does not increase the hardware cost, and does not change the attenuation of the device along with the temperature and the long time after the calibration. The calibration method has the characteristics of convenient and concise process and easy implementation.

Description

A method and system for calibrating DTOF lidar

technical field

The present invention relates to the technical field of laser ranging, and more specifically, relates to a method and system for DTOF laser radar calibration.

Background technique

Lidar is the navigation sensor of the robot. For DTOF radar, its laser emits laser pulses, and the timer records the emission time; the return light is received by the receiver, and the timer records the return time. The "flight time" of light is obtained by subtracting the two times, and the speed of light is constant, so it is easy to calculate the distance L=light speed C*flight time T/2 after the speed and time are known. However, it is affected by the device, especially the laser emission time, which is affected by the device transmission time delay and temperature, and it will be difficult to measure accurately. Therefore, it is necessary to find a reference position point to ensure the accuracy of ranging.

At present, there are generally two ways for DTOF lidar to record the laser emission time. The first one is to use two receiving devices, one is the reference receiver and the other is the main receiver. , to form the start time point of emission; the other is to use circuit feedback to emit laser, and the voltage of the laser emission drive circuit will change, which is input to TDC as the start time. One of the two needs to increase the reference receiving device, and the cost is higher , the other requires the use of drive feedback and will be affected by device temperature drift, so the above two methods have certain deficiencies.

Contents of the invention

In order to solve the above shortcomings, the present invention first proposes a DTOF lidar calibration method, which can accurately record the laser emission time point and avoid the device being affected by temperature.

The invention also proposes a DTOF lidar calibration system.

In order to achieve the above object, the technical solution of the present invention is:

A method of DTOF laser radar calibration, its implementation steps are:

(1) Add a protective cover: add a protective cover at a distance of R from the DTOF lidar;

(2) Obtain the reference signal and target position signal: DTOF laser radar emits laser pulses, and the photon detector detects and stores the reflection signal of the protective cover and the target position as a reference signal T1 and target position signal T2;

(3) Calculate and obtain the actual distance of the target object: Based on the TDC of the laser radar, the distance resolution per unit time difference is LSB, and the following formula is used to calculate the actual distance of the target object and complete the calibration; L=(T2-T1)*LSB+R.

Specifically, this calibration method is to add a protective cover outside the DTOF lidar. After the laser is emitted, a certain amount of light will be reflected back by the cover, which will form a peak at the near end of the histogram. The system uses the reflected signal of the cover As a reference signal, by corresponding the peak value with the actual distance, you can get the corresponding relationship between the peak position and the distance of a histogram, and the difference between the subsequent actual ranging peak value T2 and this peak value T1 is multiplied by the distance of the histogram The actual value of the distance measurement can be obtained by adding the radius of the cover to the unit, and the calibration is completed.

Preferably, obtaining the reference signal and the target position signal in the step (2) is specifically: after the laser radar emits laser light, the photon detector collects and stores the number of photons and the corresponding time, generates a time-of-flight histogram, and analyzes the photon in the histogram The first and second peaks are respectively used as reflection signals of the protective cover and the target position and stored.

Preferably, the first and second peaks with the number of photons in the histogram obtained from the analysis are respectively stored as reflection signals of the protective cover and the target position, and the peak finding method is to filter according to the time-of-flight histogram to obtain the filtered histogram Figure: Find the peaks of the histogram, and get the photon flight times T1 and T2 corresponding to the first and second peaks.

Preferably, the photon detector is one of SiPM detector, APD detector and SPAD detector.

A system for DTOF lidar calibration, comprising: a laser transmitter, a processor, a photon detector, a time-to-digital converter TDC and a memory, the laser transmitter, the TDC and the memory are connected to the processor, and the photon detection Connector to TDC;

The processor is used to control the laser transmitter to periodically emit laser pulses to the target object; the processor is also used to save the generated direct time-of-flight histogram according to the number of photons and corresponding time, and perform peak-seeking operations according to the histogram , get the photon flight time corresponding to the first and second peaks;

The photon detector is used to detect photons, and the photons are from the scene where the target object is located;

The TDC is used to record the time-of-flight of photons detected by the photon detector;

The memory is used to save the flight time of the photon according to the control of the processor.

A computer device includes a memory and a processor, the memory stores a computer program, and the processor implements the DTOF laser radar calibration method when executing the computer program.

A computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the described method for DTOF lidar calibration is realized.

Compared with prior art, the beneficial effect of the present invention is:

The invention uses the radar cover to complete the distance calculation and calibration of the DTOF laser radar, without increasing the hardware cost, and the calibration does not change with the temperature and the attenuation of the device after a long time. The calibration method of the invention has the characteristics of convenient, concise and easy implementation.

Description of drawings

Figure 1 is a simplified diagram of the calibration method of DTOF lidar.

Figure 2 is a histogram obtained by using the DTOF lidar calibration method.

Figure 3 is a schematic diagram of the histogram fitting FIT obtained by using the DTOF lidar calibration method.

FIG. 4 is a flow chart of the implementation of the method for DTOF lidar calibration.

FIG. 5 is a schematic diagram of a DTOF receiving SOC structure.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

As shown in Figure 1-4, a DTOF lidar calibration method, the implementation steps are:

(1) Add a protective cover: add a protective cover at a distance of R from the DTOF lidar;

(2) Take the reference signal and target position signal: DTOF laser radar emits laser pulses, and the photon detector detects and stores the reflected signal of the protective cover and the target position as a reference signal T1 and target position signal T2;

(3) Calculate and obtain the actual distance of the target object: Based on the TDC of the laser radar, the distance resolution per unit time difference is LSB, and the following formula is used to calculate the actual distance of the target object and complete the calibration; L=(T2-T1)*LSB+R.

This calibration method is to add a protective cover outside the DTOF lidar. After the laser is emitted, a certain amount of light will be reflected back by the cover, which will form a peak at the near end of the histogram. The system uses the reflected signal of the cover as a reference Signal, by corresponding the peak value with the actual distance, you can get the corresponding relationship between the peak position and the distance of a histogram, and then make the difference between the actual ranging peak value T2 and this peak value T1, and then multiply it by the distance unit of the histogram plus The radius of the cover can be used to obtain the actual value of the distance measurement and complete the calibration.

In this embodiment, the acquisition of the reference signal and the target position signal in step (2) is specifically: after the laser radar emits laser light, the photon detector collects and stores the number of photons and the corresponding time, generates a time-of-flight histogram, and analyzes the histogram to obtain The peaks with the number of photons being the first and second are respectively used as reflection signals of the protective cover and the target position and stored.

In this embodiment, the peaks with the first and second photon numbers in the histogram obtained from the analysis are respectively stored as reflection signals of the protective cover and the target position, and the peak finding method is to filter according to the time-of-flight histogram to obtain the filtered The final histogram; find the peak of the histogram to obtain the photon flight times T1 and T2 corresponding to the first and second peaks.

In this solution, the DTOF lidar has an outer cover, a processor on the PCB, and a memory. After starting to work, the laser transmitter starts to emit, and the TDC starts timing. After multiple emissions, a histogram will be formed. The histogram is stored in the receiving chip. The processor MCU Or the DSP starts to look for the first radar cover peak T1 through time-correlated single photon counting (TCSPC) technology, and stores and records it, and then searches for the peak T2 reflected by the target bit. The radius of the radar cover is R, and LSB is the minimum of the lidar TDC. resolution, so the actual distance of the target is obtained L=(T2-T1)*LSB+R.

Specifically, the radius R of the radar cover is 25mm, and the peak fitting of the histogram finds the positions of the two peak points. T1 is 100.0 and T2 is 200.5. The TDC resolution used internally is 100ps, and the minimum resolution LSB of the distance measurement is 0.5* 100ps*300000000m/s=15mm, the first peak is the reflection of the radar cover, and the second peak is the reflection of the target, so the actual distance of the target is L=(200.5-100.0)*15+25=1532.5mm, In order to realize the calibration of the radar and obtain the correct ranging value, the weighted centroid method can be used for the histogram fitting to obtain the sub-resolution histogram peak position and improve the accuracy.

In this embodiment, the photon detector is one of SiPM detector, APD detector and SPAD detector.

As shown in Fig. 5, a kind of system of DTOF lidar calibration includes: laser emitter, processor, photon detector, time-to-digital converter TDC and memory, and described laser emitter, TDC and memory are connected with described processor, The photon detector is connected to the TDC;

The processor is used to control the laser transmitter to periodically emit laser pulses to the target object; the processor is also used to save the generated direct time-of-flight histogram according to the number of photons and corresponding time, and perform peak-seeking operations according to the histogram , get the photon flight time corresponding to the first and second peaks;

The photon detector is used to detect photons, and the photons are from the scene where the target object is located;

The TDC is used to record the time-of-flight of photons detected by the photon detector;

The memory is used to save the flight time of the photon according to the control of the processor.

A computer device includes a memory and a processor, the memory stores a computer program, and the processor implements the DTOF laser radar calibration method when executing the computer program.

A computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the described method for DTOF lidar calibration is realized.

The embodiments of the present invention described above are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims (7)

1. a method for DTOF lidar calibration, is characterized in that, its realization step is: (1) Add a protective cover: add a protective cover at a distance of R from the DTOF lidar; (2) Obtain the reference signal and target position signal: DTOF laser radar emits laser pulses, and the photon detector detects and stores the reflection signal of the protective cover and the target position as a reference signal T1 and target position signal T2; (3) Calculate and obtain the actual distance of the target object: Based on the TDC of the laser radar, the distance resolution per unit time difference is LSB, and the following formula is used to calculate the actual distance of the target object and complete the calibration; L=(T2-T1)*LSB+R. 2. The method for DTOF lidar calibration according to claim 1, characterized in that, obtaining the reference signal and the target position signal in the step (2) is specifically: after the laser radar emits laser light, the photon detector collects and stores photons The time-of-flight histogram is generated, and the peaks with the first and second photon numbers in the histogram are analyzed and stored as the reflection signals of the protective cover and the target position respectively. 3. the method for DTOF lidar calibration according to claim 2, it is characterized in that, described analysis obtains photon number in the histogram and is the peak value of the first and second respectively as the reflected signal of protective cover and target position and stores, and its The peak finding method is to filter according to the time-of-flight histogram to obtain the filtered histogram; to find the peak of the histogram to obtain the photon flight times T1 and T2 corresponding to the first and second peaks. 4. The method for calibrating DTOF lidar according to claim 1, 2 or 3, wherein the photon detector is one of a SiPM detector, an APD detector, and a SPAD detector. 5. A system of DTOF lidar calibration, is characterized in that, comprises: laser emitter, processor, photon detector, time-to-digital converter TDC and memory, described laser emitter, TDC and memory and described processor connected, the photon detector is connected to the TDC; The processor is used to control the laser transmitter to periodically emit laser pulses to the target object; the processor is also used to save the generated direct time-of-flight histogram according to the number of photons and corresponding time, and perform peak-seeking operations according to the histogram , get the photon flight time corresponding to the first and second peaks; The photon detector is used to detect photons, and the photons are from the scene where the target object is located; The TDC is used to record the time-of-flight of photons detected by the photon detector; The memory is used to save the flight time of the photon according to the control of the processor. 6. A computer device, comprising a memory and a processor, the memory stores a computer program, wherein the processor implements the method for DTOF lidar calibration according to any one of claims 1 to 4 when executing the computer program. 7. A computer-readable storage medium on which a computer program is stored, wherein the computer program is executed by a processor to implement the method for DTOF lidar calibration according to any one of claims 1 to 4.

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